Why do we use a definite article before the word "Philippines?" Does that mean that "Philippines" is the short for "the Republic of the Philippines" or since it is a group of islands?
My guess is a group of islands.
Martin English has posted the below lesson regarding articles usage.
London English Classes: "A"? "An"? "The"? nothing? ("The English is the crazy")
With geographical names, there is often a definite article; you just have to learn them. Something to watch for is that your language may attach an article but English doesn't: o Brasil is just 'Brazil'. Sometimes an article gets automatically tacked on to a place-name (though this doesn't happen so much in English - examples that spring to mind are 'Le Havre' and 'O Porto' [the interesting there is that they elide with other words - au Havre, no Porto - but there's the possibility that I'm starting to talk to myself... ).
The only city that I can think of whose English name begins with an article is The Hague.
There is also "The Netherlands" and "The Ukraine" as countries with articles.
Ukraine officially dropped the article in 1993.
That's nice for them, but I think most people here would still use it. Old habits die hard.